1. Field of the Invention
The present invention relates to an inspection method and inspection apparatus for inspecting the electrical characteristics of an inspection object. More specifically, the invention relates to an inspection method and inspection apparatus capable of inspecting the electrical characteristics of an inspection object such as a device (for example, a power transistor) or each inspection object of plural devices formed on a single substrate.
2. Description of the Related Art
Upon inspecting the electrical characteristics of a device such as a power transistor, a large current and voltage are applied. For the purpose, it is necessary to bring probes into contact with electrodes of the device securely. In case of a device such as a power transistor, a stage, on which an inspection object is to be mounted, is electrically connected with an electrode (for example, a collector electrode) formed on the rear face of the inspection object. When, in this state, the electrical characteristics of the inspection object are inspected, the surface of the stage needs to be brought into secure contact with the collector electrode formed on the rear face of the inspection object.
Patent document 1 and patent document 2 disclose a technology for bringing the surface of a stage into electrical contact with a collector electrode formed on the rear face of an inspection object.
According to the technology described in patent document 1 (Jpn. Pat. Appln. KOKAI Publication No. 63-258036) (claim and page 2, upper right column, line 2 to lower left column, line 7), voltage applying electrodes for applying a voltage to a semiconductor wafer and voltage measuring electrodes for measuring a voltage of the semiconductor wafer are provided on the mounting surface of the stage. In this stage also, at least some of the voltage applying electrode and the voltage measuring electrodes are formed in the form of a belt. These electrodes are disposed alternately on the mounting surface of the stage. Such a configuration prevents a difference from occurring in a measuring result due to a difference in position of the semiconductor wafer in which a plurality of semiconductor chips have been formed.
Patent document 2 (Jpn. Pat. Appln. KOKAI Publication No. 2-166746, claim and page 2, upper right column, line 17 to page 3, upper left column, line 3) discloses the same kind of a stage as that disclosed in patent document 1. The mounting surface of the stage is divided into 2N (N is an integer of 2 or more), and voltage applying electrodes and voltage measuring electrodes are formed alternately on each division. The stage can exert the same operation and effect as those of the patent document 1.
Patent document 3 (Jpn. Pat. Appln. KOKAI Publication No. 11-64385 (claim and paragraphs [0006] to [0007]) discloses a technology concerning a probe. By this technology, connection pads of a device and probes are Kelvin-connected. Two probes are disposed in the vicinity of each other such that each of them can be electrically connected to a single connection pad. When the probes are pressed by the connection pad so that both of them make contact with each other, the probes are deformed elastically and make contact with the connection pads with tips of the two probes approaching with a fine interval.
The inventions described in the patent documents 1 and 2 can reduce the bad influence of the internal resistance of the collector electrode upon a measurement result when the collector electrodes formed on the rear face of a plurality of power devices and two kinds of electrodes formed on the mounting surface of the stage are electrically connected. However, no measure concerning connection of the probes and the electrodes of the device is taken. Therefore, by pressing the probes against the electrodes in the same manner as in the prior art, an oxide film on the electrode is scraped away and the probes are brought into electrical contact with the electrodes. Thus, there is a fear that the probes and electrodes may be damaged. If the size and the depth of a probe trace are limited in order to avoid a failure in a bonding process in the case of a power device, contact between the probes and the electrodes becomes unstable. Consequently, when a large current is applied, sparking occurs, thereby possibly damaging the probes. A loss that occurs in the electrical path between the probes and the electrode induces malfunction or the like, rendering accurate inspection impossible.
Although the probes described in patent document 3 can prevent the influence of foreign matter adhering to the probes, the probes are pressed against the connection pad conventionally, in order to bring the connection pads and the probes into contact with each other. As a result, the same problem as technology of patent document 1 exists.